In this question, we have 8.1*10^24 particles of C4H8O4, we need to find the number of moles present in this amount of particles:
1 mol = 6.022*10^23
x moles = 8.1*10^24
x = 13.45 moles of C4H8O4
Now using its molar mass, 120.1g/mol, we will find the final mass:
120.1g = 1 mol
x grams = 13.45 moles
x = 1615 grams of C4H8O4